The present invention relates generally to transfer cases for use in four-wheel drive vehicles and, more particularly, to a variable ratio range gearset for transfer cases.
In general, power transfer mechanisms, such as transfer cases, are operatively associated with both manual and automatic transmissions for directing power to the non-driven wheels of a motor vehicle for establishing a four-wheel drive mode.
Many automotive transfer cases are equipped with a speed reduction gear assembly or the like for providing xe2x80x9chigh: and xe2x80x9clowxe2x80x9d speed ranges in conjunction with the two-wheel drive and four-wheel drive operating modes. As such, a range shift mechanism is typically provided for operatively shifting components of the speed reduction gear assembly between a high-range position and a low-range position. One example of a transfer case incorporating a speed reduction gear assembly is shown in U.S. Pat. No. 5,346,442 wherein a synchronized range shift arrangement allows xe2x80x9con-the-movexe2x80x9d shifting from a low-range operating mode to a high-range operating mode while the vehicle is in the four-wheel drive mode. While such a synchronized range shift system has proven to be an improvement over traditional four-wheel drive transfer cases which required the stopping of the vehicle to shift from high-range to low-range while in the four-wheel drive mode, the teaching however still provides a bifurcated speed range arrangement.
As such, the need exists for the development of a range control system for use with gear reduction units which can establish variable torque reduction ratios between high and low limits.
In view of the foregoing, it is an object of the present invention to provide a range shift system for a gear reduction unit which can continuously vary the reduction ratios between high and low operating levels.
It is another object of the present invention to incorporate the variable range shift system and gear reduction unit into transfer cases for use in four-wheel drive vehicles.
As a related object, the variable range shift system can be arranged to permit the vehicle operator to select between distinct high and low speed ranges or operate in an adaptive mode where the speed range is automatically varied between the high and low range operating modes in response to vehicular operating and/or road conditions to improve the vehicle""s tractive performance.
Accordingly, the variable range shift system of the present invention includes a mechanism for selectively rotating a component of the gear reduction unit to vary the torque transferred from the input shaft to the output shaft. More particularly, the range shift system includes a drive mechanism including a unique worm/worm gear transmission which is operatively coupled to a carrier member of the gear reduction unit. When the drive mechanism is held fixed, the carrier does not rotate and there is no reduction between the input and output shafts. However, when the drive mechanism is rotated, the carrier is rotated relative to the input shaft which functions to change the torque transferred to the output shaft. By varying the relative rotational velocity of the carrier member, it is possible to vary the torque transfer ratio of the transfer case.
Preferably, the drive mechanism includes a variable speed motor having an output arranged to drive the worm/worm gear transmission so as to control rotation of the carrier associated with a planetary gear reduction unit. A control system is provided to control actuation of the motor in response to operating characteristics of the vehicle.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.